Before starting, lets say I have been using Magic Lantern for about three months now in my 5D Mark II, a completely new machine after it, even if I'm basically using it for its ETTR and RAW histogram, exposure was never easier (I just do landscape photography...).

Now, I think that you are reading contradictory information about the support of 6D or not because there is no official support yet. Latests "official" version of ML is from last year, no 6D back them. The dev builds of ML nowadays support ML, but those are supposed not to be 100% stable, or at least the devs does not assure you that they are 100% stables. I have been used one of those for the last months in my 5D without problem (ETTR and RAW histograms are not supported by the last year official release).

In the ML forums there is a thread about how to install ML in a 6D using one of the dev versions, with users that have tried, you can try it at your own risk (well... at your camera risk): http://www.magiclantern.fm/forum/index.php?topic=5530.0 (the second post has the instructions).

You can use any OS to do this, Windows, Mac OS X, Linux... you just need to be able to write some files into a memory card. Read the instructions that they say in the forum, but as personal notes: make sure first that you have installed the right version of the Canon official firmware before trying to install ML. And for any firmware installation, make sure your battery is fully charged.